Built GX390 help

CrewCabDart

New member
Hey all! I have acquired this Honda GX390 with a go kart I recently bought and after looking into it more I’m intrigued. If anyone could possibly help me determine what the hp number could be and maybe the value of the engine that would be great! I’m very new to these GX390s so all I could really do is look for part numbers.

From what I can tell the parts list includes:
ARC Billet flywheel

ARC Billet rod

Parsons Billet side cover

Parsons Billet valve cover

Parsons Billet carburetor adapter

Parsons 390 lift 246 duration cam

Raceseng GX390 V2 1.3 Billet rocker arms

Mikuni High Performance 38mm super BN carb

Bully Turbo 4 disc clutch

Obviously it’s has some kind of dual spring setup and what looks to be chromoly pushrods?

Any help on determining the value/ hp numbers would be great!!
 

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Jake3890

Member
That’s going to be a small block open/open motor from the looks of it and not knowing anything else it’s 20+ hp and to build something like that 2,000-2,500 sometimes more just all depends what’s all been done to the head/ porting looks like a good find this is all just my opinion have a good day
 
Last edited:

CarlsonMotorsports

Site Supporter
A GX390 is considered a big block. It should make around 30-35CHP and costs around $2800 to build brand new.
That's a fairly small cam for that big of carb, so likely someone has replaced the carb at some point. Don't know what size valves you've got and how much welding has been done to the head, but a fairly conservative dyno will place similar builds with a 33mm Mikuni at 30-32CHP.


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Carlson Racing Engines
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Jake3890

Member
Hey all! I have acquired this Honda GX390 with a go kart I recently bought and after looking into it more I’m intrigued. If anyone could possibly help me determine what the hp number could be and maybe the value of the engine that would be great! I’m very new to these GX390s so all I could really do is look for part numbers.

From what I can tell the parts list includes:
ARC Billet flywheel

ARC Billet rod

Parsons Billet side cover

Parsons Billet valve cover

Parsons Billet carburetor adapter

Parsons 390 lift 246 duration cam

Raceseng GX390 V2 1.3 Billet rocker arms

Mikuni High Performance 38mm super BN carb

Bully Turbo 4 disc clutch

Obviously it’s has some kind of dual spring setup and what looks to be chromoly pushrods?

Any help on determining the value/ hp numbers would be great!!
Definitely listen to Carlson he knows a lot very helpful all the time good luck
 
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